Electric DC motors have experienced difficulty in finding acceptance in certain types of applications requiring a high operating torque, such as vehicles, lawn mowers and certain types of tools. Until the present invention, it was not possible to achieve sufficient torque and reasonable efficiency with a machine of sufficiently compact size. Efficiency is particularly important because of the relatively limited nature of the DC power source, typically a battery.
U.S. Pat. No. RE. 33,628 issued on Jul. 2, 1991, discloses a particularly efficient electro mechanical machine which has a field producing assembly, which serves as a stator and is mounted in a housing so as to define an axial air gap which is circumferentially disposed about an axis of rotation. The field assembly is structured to produce a circumferential distribution of magnetic flux in the air gap having P periodic extremes of flux density about the axis. A disc-shaped electrical assembly, serving as an armature is positioned in the air gap, and mounted so that the armature and field assembly are rotatable relative to each other. The armature has a circular array of C non-overlapping coils on each of its front and back faces, the coils on one face being angularly offset from the coils on the other face and each having the same arcuate extent, smaller than 360 degrees divided by P. The coils are arranged in groups of serially connected coils with each group occupying an unique area of an armature face. Inasmuch as adjacent coils are exposed to opposite extremes of the flux, they must have current flow in opposite directions. This is achieved by winding adjacent coils in opposite directions.
The present invention realizes improvements to the machine disclosed in U.S. Pat. No. RE 33,628 which substantially increases the torque. Specifically, the structure of the armature is modified, so as to halve the number of parallel circuits without reducing the number of coils, which substantially reduces the rotational speed, increasing the torque. In addition, the commutation system, which couples power to the motor, is modified to increase the percentage of time all of the coils in the armature are energized. Increased torque at a given horsepower means that torque requirements can be met by smaller, lower power motors. The savings in cost, weight and size are significant, not to mention the more efficient use of energy.